Fuel metering device



NOV. 8, 1949 w, H P 2,487,774

FUEL METERING DEVICE Filed Nov. 1'7, 1943 2 Sheets-Sheet 1 lNVENTOR ATTORNEY Patented Nov. 8, 1949 UNITED STATES PATENT OFFICE FUEL METERING DEVICE Pieter W. Schipper, Manchester, Conn. Application November [7, 1943, Serial No. 510,647

18 Claims.

This invention relates to a fuel metering device for internal combustion engines, such as carbu retors and fuel iniectors, in which the fuel for combustion is delivered under pressure in amounts varying in proportion to variations in the quantity of air flowing through the air passage means to the engine.

In the fuel metering devices now in use, the stream of air flowing to the engine is used to set up a differential of pressures which acts on suitable pressure responsive means for controlling a fuel pressure regulator, the usual air metering device being a venturi located in the air passage which provides a differential of throat and scoop pressures proportional to the air flowing through the passage. This differential pressure acts on a diaphragm for controlling the fuel pressure regulating valve in the case of a carburetor or in the case of a fuel injector may, for example, act to vary the cutoff of a fuel injection pump.

These devices have the disadvantage that at best they can provide the desired fuel to air ratio over only a part of the range of engine operation. The controlling air pressures become so small in the idling range that they will not operate the pressure responsive mechanism and consequently a special fuel metering device must be provided to enable the engine to run at idling speeds. Also, at high power outputs of the engine, another special fuel metering device must be provided to supply additional fuel to the engine to protect the latter against detonation and overheating. Still another device is required to correct for temperature and density changes due, for example, to changes in altitude.

It is a further disadvantage of the pressure type carburetors now in use that, due to the required mechanical interconnection of the air and fuel pressure responsive elements, these are necessarily built into a compact unit within the limits of space available and they are unable to measure air flow accurately. This is due in part to the fact that the air section including the venturi is short and includes sharp bends in the vicinity of the venturi with the result that interference with the air flow measurement occurs from stratification and turbulence in the air stream. A further disadvantage results from concentration of weight. Carburetors of such type now in use 2 weigh fifty pounds, often more, and this concentration of weight which must be supported in overhanging position is not only generally undesirable but it aggravates the already difficult vibration problems present in mounting airplane engine carburetors.

One of the objects of the present invention is 0 provide a charge forming device for internal combustion engines in which any variation from a constant fuel to air ratio in the idling and full power range and also the compensation for Mach number, fuel viscosity, orifice coefficient, and temperature and density variations are functions of the basic metering system, thus greatly simplifying the device by eliminating all supplementary fuel metering devices such as idling and economizer valves and their operating mechanisms and temperature and pressure corrective devices.

Another object of the present invention is to provide greater flexibility in the location of the air and fuel meterin sections of the device, permitting great freedom in design and eliminating the present concentration of weight.

A further object of the invention is to provide fuel-air balancing sections for a pressure type carburetor having a minimum of friction and inertia.

A still further object of the invention is to provide greater sensitivity in the fuel and air metering sections of such a carburetor enabling even the low differentials of air pressures experienced in the idl ng range to meter the fuel and meter it accurately.

A yet further object of the invention is to provide a pressure type carburetor in which the fuel pressure regulator is controlled by air pressures set up in a venturi in the air passage means which can be located in the horizontal section of the air inlet system remote from the fuel metering section of the carburetor to provide a smooth approach to the venturi at opposite ends thereof and thus avoid stratification and turbulence of the air in the vicinity of the venturi.

A further object of the invention is to provide a charge forming device in which the various pressures in the air and fuel sections are converted into electrical energy by pressure-electric units of a type in which the relationship of electrical variation in the electric element and pressure variation in the pressure element of the unit may be varied to provide any desired devia-' electrical characteristics change in response to changes in fuel and air pressures.

A further object is generally to improve the construction and operation of charge forming devices.

Other objects and advantages of the invention will be apparent from the following detailed description of a specific embodiment thereof in a pressure type carburetor diagrammatically illustrated in the accompanying drawings.

In the drawings, wherein similar characters of reference refer to similar parts throughout the several views:

Fig. 1 is a diagrammatic view showing one application of the present invention to pressure type carburetors;

Fig. 2 is a wiring diagram showing the connections of the balanced sections of the carburetor in a Wheatstone bridge circuit;

Fig. 3 is a view showing diagrammatically one advantageous physical separation of the several sections of the carburetor;

Fig. 4 is an enlarged detail of a part of a pressure-electric unit;

Fig. 5 is a diagrammatic illustration of a modified electric element for use in direct current circuits;

Fig. 6 is a view similar to Fig. 2 modified to utilize the direct current element of Fig. 5; and

Fig. '7 illustrates a fuel-air curve obtainable as a result of the basic metering functions of the device.

Referring to Fig. 1, it will be observed that the pressure type carburetor diagrammatically illustrated therein, includes the venturi ill for metering the quantity of air supplied through an air passage I2 to the engine, a throttle [4 being provided in the passage downstream from the venturi. The carburetor also includes the constant pressure fuel pump [6 which supplies fuel from the tank l8 through conduits 20, 22 and 24, valve casing 26, and conduit 21 to unmetered fuel chamber 28, a balanced by-pass valve 38 being provided in valve casing 26 having the valve actuating stem 32 depending therefrom. The bypassed fuel is returned through a conduit 33 to the tank IS. A fixed fuel metering orifice 34 is provided between the unmetered fuel chamber 28 and a metered fuel chamber 36 which supplies fuel through a conduit 38 to the discharge nozzle 48 in air passage l2, all in a usual manner.

In accordance with the present invention, the balanced sections of the carburetor include four pressure-electric units Pl, P2, P3 and CT which, as shown most clearly in Fig. 2, are connected in Wheatstone bridge arrangement, each unit comprising one arm of the bridge. Alternating current voltage is supplied through conductors 42 and 43, a half-wave rectifier 44 being connected in conductor 43 for converting the alternating current to intermittent direct current at points A and C of the bridge.

The unit PI is responsive to the diiferential of unmetered and metered fuel pressures in the chambers 28 and 36 respectively; the unit P2 is responsive to the venturi throat and scoop pressures in the passage l2 upstream from the throttle l4; the unit P3 is responsive to pressures in the air passage I2, and as shown is connected to the throat of the venturi; and the unit CT is responsive only to the temperature of the air in the air passage I2. It will be noted that these four units are so disposed in a Wheatstone bridge arrangement that the units PI and P2 comprise one side of the bridge including the point B, while the units P3 and CT comprise the other and parallel side of the bridge including point D. Thus, when the impedance of PI bears the same relation to the impedance of P2 as the impedance of P3 bears to the impedance of CT, it will be evident that the voltage at the points B and D will be equal and that no current will flow through the servo mechanism, hereinafter described, which is connected across the points B and D.

The pressure-electric units Pl, P2, P3 and CT are similar in structure, except for minor variations afiecting the electrical characteristics of their electric elements. Accordingly, a detailed description of one of these units will sufllce. Referring particularly to the pressure-electric unit PI, shown in section in Fig. 1, it will be noted that this unit consists of a U-shaped core member 46 having a relatively wide air gap 48. therein. The core 46 carries a winding 58 which is connected by conductors 52 and 54 to the points A and B respectively of the bridge. A member 56 is adapted to be moved into and out of the gap 48 to vary the reluctance of the magnetic circuit including the core 46. This member may be of any suitable material which has a higher permeability than air,-for example, a. material which will give the desired variation in reluctance in the magnetic circuit to give suflicient variation in the inductance of coil 50 to provide the desired change in impedance in this arm of the bridge. The member 56 is preferably contoured to provide a non-linear variation in the impedance across points A and B as the member 56 is moved into the air gap. The member 56 may assume various shapes to get different variations in impedance. As herein shown, this member is provided with tapered side walls 58 (Fig. 4) so that the gap is closed progressively more rapidly as the member is moved into the space between the pole faces of the core.

Pressure responsive means are provided for moving the member 56 into and out Of the air gap 48 in accordance with pressure changes in the unmetered and metered fuel chambers 28 and 36, respectively. This pressure responsive means comprises a housing havin two complemental parts 60 and 62 divided into two fluid tight chambers 12 and 14 by a diaphragm 16,.the periphery of which is clamped between flanges 18 on abuting parts of the housing. The diaphragm 16 carries a rod 80. which extends through and is fixed to diaphra-gms 82 and 84 constituting the opposite end walls of the housing and permits a limited, unrestrained movement of the diaphragm l6 and rod 88 and consequently oi the member 56 which is carried at the free end of the rod 88 externally of the housing. A spring 86, the deflection characteristics of which may be varied to suit the requirements of different units, is disposed in chamber 14 and has one end bearing against diaphragm l6 and its other end bearing against an inwardly directed peripheral flange 88 of the housing part 62. It will be evident that with the unmetered fuel pressure, in chamber 28 and the metered fuel pressure in the chamber 36 communicating with chambers I2 and I4 through conduits 80 and 92 respectively, the member 56 will be moved in a direction longitudinally of the rod 80 by changes in the differential of unmetered and metered fuel pressures.

The units P3 and P2 are identical with the unit PI above described, with the exception 01 possible minor variations in the deflection characteristics of their springs 88 and variations in the contour of their members 56 for the purpose of altering the variations in electric characteristics of their respective units for purposes more fully pointed out hereinafter.

The unit CT is identical with unit PI above described, except that the chamber I2 of this unit is evacuated to eliminate temperature responsiveness of this chamber, and the spring 86 thereof is disposed on the opposite side of diaphragm I6 and biases the latter in the opposite direction. The member 56 associated with this unit has its direction of movement correspondingly reversed. Also the chamber I4 may oontain a suitable expansible fluid which is critical within the range of air temperatures encountered in the operation of the device. The chamber I4 of unit CT, as shown, projects into the air stream in the passage I2 so that this unit will be responsive to temperature changes only of the air entering the engine.

The unit P3 has its diaphragm I6 responsive to throat pressure in the annular passage 94 which communicates through a plurality of radial passages 96 with the throat of the venturi I0, this pressure being communicated through a conduit 98 to the chamber I2 of this unit. Obviously, this chamber I2 might be connected with the air pressure in the passage I2 at some other point upstream of the throttle I4. The chamber I4 of unit P3 is evacuated so that the position of member 56 is controlled solely as a function of absolute pressure.

The diaphragm of the unit P2 is subjected to the differential of throat and scoop pressures of the venturi, the pressure in scoop I being communicated to chamber I2 by a conduit I02 while the pressure in the throat chamber 94 is communicated by conduits 98 and I04 to chamber I4.

The unit P3 has the free ends of its coil 50 connected by conductors I 06 and I08 to points A and D of the bridge respectively; unit P2 has the free ends of its coil 50 connected through conductors H0 and II2 with points B and C respectively of the bridge, while the unit CT has the free ends of its coil connected through conductors H4 and I6 with points D and C respectively Of the bridge.

The fuel regulating valve 30 has a solenoid core H8 on its stem 32 which has its opposite ends extending into a Pair of servo coils I and I22. These coils are energized from amplifiers I24 and I26 in parallel conductors I28 and I30 (Fig. 2) connected across the points B and D of the bridge. Further, the conductor I28 is provided with a half-wave rectifier I32 which permits current to fiow only from B to D, while the conductor I30 is provided with a similar rectifier I34 which permits current to flow only from D to B.

A variable resistance I 35 is connected across the points B and C in parallel with the coil 50 of unit P2, providing manual means for varyin the impedance of this arm of the bridge independently of the operation of the unit P2.

In the operation of the carburetor, the pump I6 supplies fuel from the reservoir I8 through conduits 20, 22 and 24 and the valve housing 26 and conduit 21 to the unmetered fuel chamber 28. The pressure in the chamber 28 is varied by the position of the by-pass valve 30 which maintains the necessary pressure of unmetered fuel as a result of variations in the amount of fuel bypassed through conduit 33 to the reservoir. Fuel flows in the usual manner through an orifice into the metered chamber 30 and through the fuel passage 38 to the discharge nozzle 40 into the air stream.

Changes in the differential of air pressures in the throat and scoop which affect the pressure responsive diaphragm I6 of unit P2 will cause a change in the impedance of the circuit including coil of this unit which will unbalance the bridge circuit and cause current to flow from B to D through conductor I28 or from D to B through conductor I30 as determined by the condition of unbalance, thus to cause the by-pass valve 30 to change the fuel pressures in fuel chambers 36 and 28 which are acting upon the pressure responsive diaphragm I6 of unit PI, until the balance is again restored in the bridge at the new value of air flow.

Similarly, changes in pressure in the air passage l2 which affect the pressure responsive element I6 of unit P3 or changes in temperature of the air in the air passage affecting the diaphragm 16 of the unit CT, control the valve 30 and vary the pressure of the fuel in chambers 28 and 36 to correct the fuel supplied to the engine in accordance with these variations to maintain the desired fuel-air ratio.

As a specific illustration, if the throttle I4 in Fig. l is moved in an opening direction from the throttled position shown in this figure, the increased air flow in the air passage I2 will result in an increase in the differential of throat and scoop pressures affecting unit P2 and will cause the diaphragm I6 thereof to move the member 56 to the right, as indicated by the arrow :c. As the member 56 enters the gap, the reluctance of the magnetic circuit including the core 46 is progressively decreased with a resultant increase in inductance in the coil 50. Thus, the impedance of the arm BC of the bridge increases with increasing air flow, and the bridge is unbalanced, causing a flow of current from D to B through conductor I30 to energize servo coil I22 and cause the valve 30 to admit more fuel to chamber 28 and by-pass less fuel through the conduit 33. At the same time P3 will move its member 56 to the left (Fig. 2) with a corresponding change in the impedance of the arm AD. When the increase in the differential of pressures in chambers 28 and 36 has increased sufliciently, the impedance in the arm A-B of the bridge will be such as to again balance the bridge with the valve 30 in its new position of increased fuel flow, 1. e. balance will be restored when the product of P CT equals the product of P P Similarly, a decrease in air flow will cause a decrease in impedance in the arm BC and an increase in the impedance of arm AD resulting in a current flow from B to D through the conductor I28 to energize coil I20 to decrease the flow of fuel to chamber 28 and by-pass more fuel through conduit 33.

It will be evident that if, for a given displacement of the diaphragm I6, the impedance and the spring tension of the unit change proportionally, the system above described would give a constant fuel air ratio as indicated by the line I38 in Fig. '7. However, by suitably changing the contour of the members I, it is posible to maintain a constant fuel-air ratio throughout idling and cruising ranges while providing a predetermined increase in the ratio of fuel to air to provide the desired enrichment at high engine outputs, as indicated at I in this figure, as a result of the basic metering functions of the device. Further, the members 56 may be so contoured that the additional fuel supplied by this so-called economizer action is also proportional to the increase in air flow through the passage l2 during the economizer range. Various other corrections can be made by varying the contour of members 56 to vary the fuel air ratio curve-as desired, these corrections being inherent in the operation of the units.

In Fig. 5 a modified construction is shown for the electrical element ofthe pressure-electric units which is suitable for the direct current circuit of Fig. 6 wherein units P4, P5, P6 and GT1 are shown in the same relative arrangement in a Wheatstone bridge circuit as the units PI, Pi,

P3 and CT occupy in Fig. 1. In Fig. 5 the unit P5 is shown for purposes of illustration. This unit includes a slider 2 carried by the external portion of rod 80 of the pressure responsive element, and a resistance I along which the slider moves to vary the resistance of the element. In this construction the variation from a constant fuel air ratio relationship is obtained by progressively increasing the length of the successive coils of the resistance to give the desired fuel air ratio curve. The slider H2 is connected with point B of the bridge by conductor I46 while the resistance element It, is connected to point C of the bridge by conductor Ill. The elements of the other units are similarly connected in their arms of the bridge. The servo-mechanism includes a conductor I50 connected acrossthe points B and D of the bridge having an amplifier I52 therein energizing a servo coil I 54. In this modified construction, the stem 32 of valve 30 is provided with a polarized core I58.

The operation of the direct current form is essentially the same as that described in connection with the Fig. ,1 construction. Any change in airflow results in a change in the product of the resistances in the-arms BC and AD of the bridge causing current to flow between the points Band D, actuating the valve 30 and changing the resistance in the arm AB until balance has been restored.

As a result of these improvements, it will be evident that a pressure type carburetor has been provided in which air pressure, throat and scoop differential pressures, air temperature and metered and unmetered fuel differential pressures are each converted into variable impedance or resistance by means of pressure-electric units; also that a carburetor has been provided in which a correct balance is provided between the four principal elements of such a pressure typ carburetor. It will further be evident that a carburetor has been provided that is capable of metering the fuel to get any desired fuel-air ratio curve by the inherent characteristics of these four elements without the necessity for providing additional fuel by such devices as idling fuel valves, economizer valves or supplementary corrective devices.

As a further result of these improvements, a charge forming device has been provided in which any desiredfuel-air ratio curve can be provided as a natural function of the basic metering system. For example, the basic metering system can be designed to include inherent compensation for changes in orifice discharge coefficient. Since this is a function of the fuel pressure drop, the electric element of the unit connected across arm A--B of the bridge would be modified. Similarly, the unit (71 can be corrected for changes in fuel density and viscomty.

By eliminating friction and inertia forces, an air responsive metering device has been provided which is capable of metering fuel at the low air flows encountered during the idling range, thus eliminating special provisions heretofore required for supplying fuel in this range.

It is a further advantage of the improved construction that the air metering and fuel metering sections of the carburetor, being no longer mechanically connected can be located remote from one another, as particularly illustrated in Fig. 3, thus providing great freedom in the design of such a carburetor and eliminating the present serious concentration of weight at an undesirable location on the engine. Further, the new freedom of location of the air metering section of the carburetor enables the venturi to be installed ahead of the carburetor elbow thus eliminating all occurrence of stratification and turbulence of the air in the vicinity of the venturi.

Further, a fuel metering device has been provided which is particularly well-adapted for mass production and one in which manufacturing limits can be greatly reduced, since electrical tolerances are much easier to maintain than dimensional tolerances. Also, uniformity of performance can be obtained on the bench without introducing fuel in the jets or air flow through the venturi.

While the invention has been illustrated in the drawings and described herein as embodied in a pressure type carburetor, it will be understood that the servo coils I20 and I22 might equally well, for example, control the cut-off mechanism of a fuel injector. It will be obvious that the construction and arrangement of the various elements may be modified in various other ways without departing from the scope of the invention.

By pressure-electric unit is meant any of the numerous devices for producing a variation in the electrical characteristics of a circuit in response to movement of a pressure responsive member. A large number of electrical gages are suitable for carrying out the invention in its broader aspects, such as piezo-electric crystals, strain gap gages and other gages which vary their electrical characteristics as a result of variations, for example, in resistance, capacity or reactance. The variable resistance and variable impedance gages disclosed herein are well-suited for carrying out the objects of the invention, but are illustrative only.

What is claimed and desired to be secured by Letters Patent is as follows:

1. In a charge forming device for internal combustion engines, an electric circuit, a plurality of pressure-electric means having their pressure elements responsive to pressure changes in the fuel and air flowing to the engine to vary the electrical characteristics of their electric elements, said pressure-electric means having their electric elements constantly connected in said circuit in normally electrically balanced relationship, valve means controlling the fuel flow to the engine, and electro-responsive means governed by unbalance of said pressure electric means due to changes in an electrical characteristic of the electric elements of said pressure-electric means for controlling the operation of said valve means to provide a predetermined fuel air ratio.

2. In a charge forming device for internal combustion engines, fuel passage means for supplying fuel to the engine having means therein for setting up a differential of pressures proportional to fuel flow therethrough, air passage means for supplying air to the engine having means therein for setting up a differential of air pressures proportional to air flow therethrough, an electric circuit, pressure-electric units having their pressure elements responsive respectively to said differentials of air and fuel pressures, said pressureelectric units having their electric elements constantly connected in normally electrically bal-' plying fuel to the engine having metering orifice means therein for setting up a differential of unmetered and metered fuel pressures, air passage means having -a venturi therein for setting up a differential of air pressures, an electric circuit, a plurality of pressure-electric units having their electric elements constantly connected in said circuit in normally electrically balanced relationship and having their pressure elements responsive to said differential pressures set up in said fuel and air passage means, said electric elements being balanced when said differential of unmetered and metered fuel pressures balances said differential of air pressures, and electro-responsive valve means responsive to the unbalance of said electric elements for varying the fuel flow to said orifice means to again balance said electric elements.

4. In a charge forming device for internal combustion engines, fuel passage means for supplying fuel to the engine having orifice means therein for setting up a differential of fuel pressures, air passage means for supplying air to the engine having a venturi therein for setting up a difl'erential of pressures proportional to air flow therethrough, valve means for controlling the fuel flow to said orifice means, electric circuit means including therein electro-responsive means for operating said valve means, and four pressure-electric units having normally electrically balanced electric elements in said circuit means for controlling the energization of said electro-responsive means and having their pressure elements responsive to pressure changes and to temperature changes in the air in said venturi, to said differential of fuel pressures and to said differential of air pressures respectively.

5. A charge forming device for an internal combustion engine including fuel and air supply passages, nornially balanced electric circuit me ns including an electro-responsive device operative to vary the flow through said fuel passage, a plurality of pressure-electric units having their pressure elements sensitive to changes in pressure of the fuel and pr; sure and temperature of the air in said passages and having their electric elements connected in normally balanced relationship in said circuit means and controlling the unbalance thereof and the energization of said electro-responsive device, said electric elements having means for varying the ratio of air to fuel supplied by said electro-responsive device at different parts of the operating range of the engine to provide a predetermined fuel-air ratio curve.

6. A charge forming device for an internal combustion engine including fuel and air supply passages, adjustable fuel feeding means, electro-responsive means for adjusting said fuel feeding means, a plurality of pressure-electric units having their pressure elements sensitive to changes in pressure of the fuel in said fuel passage and pressure and temperature of the air in said air passage and having their electric elements arranged to control the energization of said electroresponsive means, each of said units including a magnetic core having an air gap therein, a winding on said core, and a contoured member movable in said gap by the pressure sensitive element of the unit for differently varying the impedance of said core at different parts of the operating range of the engine to provide predetermined variations in the fuel-air ratio curve.

'1. In a charge forming device for an internal combustion engine, fuel metering means for setting up a differential of fuel pressures, air metering means for setting up a differential of air pressures, valve means for controlling the flow of fuel to said fuel metering means, an electric circuit, pressure-electric means having their electric elements connected in said circuit in normally balanced relation and having their pressure elements controlled by said fuel and air differential pressures and by the temperature of the charging air, and electro-responsive means for actuating said valve means energized upon unbalance of said circuit due to changes in temperature and pressure affecting the electric elements of said pressure-electric means. I

8. A charge forming device for an internal combustion engine having a fuel supply conduit, a metering orifice in said conduit creating a differential of fuel pressures variable with variations in flow therethrough, an air supply passage, means in said passage for creating a differential of air pressures variable with variations in air flow therethrough, fuel valve means for varying the supply of fuel to said metering orifice, and means for normally balancing said air and fuel pressures including an electric circuit and pressure-electric units having their respective pressure responsive means responsive to changes in said fuel and air differential pressures and having their electric elements connected constantly in said electric circuit and adapted to vary an electric characteristic of saidcircuit in response to unbalance of said differentials of fuel and air pressures, and means responsive to unbalance of said circuit due to variations in said differential of air pressures for effecting operation of said fuel valve means to vary said differential of fuel pressures to again balance the circuit at the new rate of air flow.

9. In a charge forming device for internal cornbustion engines having air and fuel metering sections, an electrical circuit comprising a Wheatstone bridge, a pressure-electric unit connected in one arm of said bridge having its pressure responsive element acted upon by metered and unmetered fuel pressures in said fuel section, a pressure-electric unit connected in another arm of said bridge having its pressure responsive element acted upon by metered and unmetered air pressures in said air section, two pressure-electric units having their electric elements connected respectively in the other two arms of said brid e.

and having their pressure elements responsive respectively to changes in the pressure and the temperature of the air in said air section, a source of electrical potential connected diagonally across said bridge in one direction, servo-mechanism connected across said bridge in the other direction and normally deenergized when said bridge is balanced, and'a valve in said fuel section controlling the fuel flow to the engine controlled by said servo-mechanism upon a change in air flow in said air section causing an unbalance of the bridge to cause a corresponding increase in fuel flow to again balance the bridge at the new air flow. V

10. Ina charge forming device for internal combustion engines having air and fuel metering sections, an electrical circuit comprising a Wheatstone bridge, a pressure-electric unit connected in one arm of said bridge having its pressure responsive element acted upon by fuel pressures in said fuel section, a pressure-electric unit connected in an adjacent arm of said bridge having its pressure responsive element acted upon by air pressure in said air section, pressure-electric units connected in each of the other arms of said bridge and having their pressure responsive elements acted upon by air pressure and air temperature of the air in said air section respectively, a source of electrical potential connected diagonally across said bridge in one direction and servo-mechanism connected across said bridge in the other direction, and a, valve operated by said servo-mechanism controlling the fuel flow in said fuel section.

11. In a charge forming device for an internal combustion engine, an air supply passage, a fuel supply passage, an adjustable fuel feeding device, and electrical apparatus for adjusting said fuel feeding device in accordance with variations in air flow through said air passage comprising, a Wheatstone bridge energized at diagonally opposite points, servo-mechanism for operating said fuel feeding device connected diagonally across said bridge in the other direction and energized in response to variations in the unbalance in the two sides of said bridge, and electric elements connected in the arms of said bridge having their electrical characteristics varied in, response to changes in pressure in said supply passages for controlling the balance of said bridge.

12. In a charge forming device for an internal combustion engine, an air supply passage, an adjustable fuel feeding device, and electrical apparatus for adjusting said fuel feeding device in accordance with variations in air flow through said air passage comprising, a Wheatstone bridge energized at diagonally opposite points, servo-mechanism for operating said fuel feeding device con- 'nected diagonally across said bridge in the other direction and energized in response to variations in the unbalance in the two sides of said bridge, and electric elements connected in the arms of said bridge having their electrical characteristics varied in response to changes in pressure in said supply passage for controlling the balance of said .bridge, said servo-mechanism including two servo coils in parallel, and a half-wave rectifier connected in series with each of said coils arranged to permit current flow in opposite directions in the respective coils, and an armature for actuating said fuel feeding apparatus in opposite directlons in response to current flow in said respective coils.

13. In a charge forming device for internal combustion engines, fuel passage means for supplying fuel to the engine having means therein for 12 setting up a differential of pressures proportional to fuel flow therethrough, air passage means for supplying air to the engine having means therein for setting up a differential of air pressures proportional to air flow therethrough, pressure-electric units having their pressure elements responsive respectively to said differentials of air and fuel pressures, and valve means for controlling the fuel flow through said fuel passage means having electro-responsive operating means governed by the electric elements of said units to provide a predetermined fuel air ratio, the electric element of each of said pressure-electric units comprising a core member having a gap, a winding on said core member, and an armature movable in said gap by the pressure-responsive element of the unit to vary the impedance of said winding.

14. In a charge forming device for an internal combustion engine, passage means for supplying .liquid fuel to the engine having means therein for measuring fuel flow by pressure drop, passage means for supplying air to the engine having means therein for measuring airflow by pressure drop, pressure and temperature of the air flowing in said air supply passage means, valve means controlling the fiow of liquid fuel to said fuel flow measuring means, electric circuit means, electro-responsive means for operating said valve means, four pressure-electric units having normally electrically balanced electric elements connected in said circuit means controlling the energization of said electro-responsive means and having their pressure elements responsive to said liquid fuel pressure drop, said air pressure drop, the pressure in said air passage and the temperature in said air passage. v

15. In a charge forming device for an internal combustion engine, passage means for supplying liquid fuel to the engine having means therein for measuring fuel flow by pressure drop, passage means for supplying air to the engine having means therein for measuring airflow by pressure drop, pressure and temperature of the air flowing in said air supply passage means, valve means controlling the flow of liquid fuel to said fuel measuring means, electro-responsive means for operating said valve means, four pressure-electric units for controlling said valve means in pre-- determined relationship to the quantity of air flowing to the engine, each of said units including a. pressure element and an electric element, said electric elements being connected in normally electrically balanced relation in the four arms of a Wheatstone bridge circuit and said electro-responsive means being connected across the normally equal potential points of said bridge circuit, and the pressure elements of said units being responsive respectively to said fuel pressure drop, said air pressure drop, the'pressure in said air passage and the temperature in said air passage.

16. In a charge forming device for internal combustion engines, passage means for supplying fuel to the engine having means therein for setting up a differential of pressure proportional to fuel flow therethrough, passage means for supplying air to the engine having means therein for setting up a differential of air pressure proportional to the air flow therethrough, pressure-electric units having their pressure elements responsive respectively to said differential of air and fuel pressures, and valve means for, controlling the fuel flow through said fuel passage means having electro-responsive operating means governed by the electric elements of said units to provide a basic fuel air-ratio, the electric elements of said pressure-electric units comprising resistance members having a unit resistance which varies at different points along their length, and said pressure elements each comprising a pressure-responsive member carrying a contact element slidable along its associated resistance, whereby the basic fuel-air ratio is varied in predetermined power ranges of the engine.

17. A fuel supply system for an intern-a1 combustion engine, comprising a conduit for combustion air flowing to said engine, means associated with said conduit for producing two unequal pressures whose difierence is a measure of the power output of said engine, means responsive to the difference of said two pressures for varying a first electrical impedance, a conduit for fuel flowing to said engine, a metering restriction in said fuel conduit, means responsive to the pressure differential across said metering restriction for varying a second electrical impedance, an electrical network including said imped-ances for balancing said impedances against each other, and means responsive to the unbalance of said network for controlling the flow of fuel through said fuel conduit so that said flow is substantially proportional to said engine power output.

18. A fuel supply system for an internal combustion engine, comprising a conduit for combustion air flowing to said engine, means associated with said conduit for producing two unequal pressures whose difference is a measure of the power output of said engine, means responsive to the difference of said two pressures for varying a first electrical impedance, a conduit for fuel flowing to said engine, a pump in said conduit, 9. metering. restriction in said conduit downstream from said pump, means responsive to the pressure differential across said metering restriction for l4 varying a second electrical impedance, means for variably restricting said fuel conduit between said pump and said metering restriction to control the flow of fuel therethrough, a relief passage extending from the outlet to the inlet of said pump, valve means in said passage and eflfective to open said passage increasingly as the fiuid flow through said conduit is reduced by said variable restricting means, an electrical network including said impedances for balancing said impedances against each other, and means responsive to the unbalance of said network for controlling said variable restricting means so that said fuel flow is substantially proportional to said engine power output.

PIETER. W. SCHIPPER.

REFERENCES CITED The following references are of record in the file of this patent:

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